Method for controlling characteristics curve shape for variable contrast photographic elements

Abstract

A process for controlling the silver halide grain-to-grain distribution of a variable contrast dye in a light sensitive silver halide emulsion layer of a variable contrast photographic element, and thereby adjusting the low contrast characteristic curve of the element, is disclosed comprising the process steps of adding a green variable contrast sensitizing dye of the following formula (I) to a silver halide emulsion for a variable contrast photographic element, adding a blue sensitizing dye of the following formula (II) to the same silver halide emulsion, and coating the emulsion on a support. In the process, the green and blue sensitizing dyes are added to the emulsion at substantially the same time, and the green dye is added in an amount less than that required to impart maximum sensitivity to all of the silver halide in the emulsion. ##STR1## In formula (I), R 1 , R 2 , R 6 and R 7 each independently represent hydrogen, halogen, hydroxy, or substituted or unsubstituted alkyl, alkenyl, alkoxy, alkylamino, alkylthio, aryl, aryloxy, arylamino or arylthio. R 3 , R 4 and R 5 each independently represent substituted or unsubstituted alkyl or aryl. X represents a counterion as needed to balance the charge of the molecule. In formula (II), Z represents the atoms necessary to complete an optionally further substituted five- or six-membered heterocyclic ring, R 8 represents substituted or unsubstituted alkyl or aryl, and R 9 represents hydrogen, substituted or unsubstituted alkyl or aryl, or a heterocycle.

What is claimed is: 
     
       1. A process for controlling the silver halide grain-to-grain distribution of a variable contrast spectral sensitizing dye in a light sensitive silver halide emulsion layer of a variable contrast photographic element comprising the process steps of: (a) adding a variable contrast sensitizing dye of formula (I) to a silver halide emulsion which comprises cubic, octahedral or spherical grains: ##STR4##  wherein R 1 , R 2 , R 6  and R 7  each independently represent hydrogen, halogen, hydroxy, or substituted or unsubstituted alkyl, alkenyl, alkoxy, alkylamino, alkylthio, aryl, aryloxy, arylamino, or arylthio; R 3 , R 4  and R 5  each independently represent substituted or unsubstituted alkyl or aryl; and   X represents a counterion as needed to balance the charge of the molecule;     (b) adding a sensitizing dye of formula (II) to the silver halide emulsion: ##STR5##  wherein Z represents the atoms necessary to complete a five- or six-membered heterocyclic ring; R 8  represents substituted or unsubstituted alkyl or aryl; and   R 9  represents hydrogen, substituted or unsubstituted alkyl or aryl, or a heterocycle; and     (c) coating the emulsion on a support; wherein the formula (I) and formula (II) sensitizing dyes are added to the emulsion at substantially the same time, and the formula (I) dye is added in an amount less than that required to impart maximum sensitivity to all of the silver halide in the emulsion.     
     
     
       2. The process of claim 1 wherein one of R 3 , R 4  and R 5  is alkyl substituted with an anionic substituent. 
     
     
       3. The process of claim 2 wherein one of R 3 , R 4  and R 5  is sulfoalkyl. 
     
     
       4. The process of claim 2 wherein R 2  is trifluoromethyl and R 7  is phenyl. 
     
     
       5. The process of claim 2 wherein Z represents the atoms necessary to complete a pyridine, oxazole, thiazole, benzoxazole, or benzothiazole ring. 
     
     
       6. The process of claim 5 wherein R 8  and R 9  each represent unsubstituted alkyl of from 1 to 4 carbon atoms. 
     
     
       7. The process of claim 5 wherein the dye formula (I) and the dye of formula (II) are in separate solutions which separate solutions are added to the emulsion. 
     
     
       8. The process of claim 5 wherein the dye of formula (I) and the dye of formula (II) are in the same solution which solution is added to the emulsion. 
     
     
       9. The process of claim 1 wherein Z represents the atoms necessary to complete a pyridine, oxazole, thiazole, benzoxazole, or benzothiazole ring. 
     
     
       10. The process of claim 1 wherein R 8  and R 9  each represent unsubstituted alkyl of from 1 to 4 carbon atoms. 
     
     
       11. The process of claim 1 wherein the dye of formula (I) and the dye of formula (II) are in separate solutions which separate solutions are added to the emulsion. 
     
     
       12. The process of claim 1 wherein the dye of formula (I) and the dye of formula (II) are in the same solution which solution is added to the emulsion. 
     
     
       13. The process of claim 1 wherein the amount of dye of formula (I) added to the emulsion is sufficient to achieve a mono-layer of dye adsorbed to about 0.5 to 20% of the silver halide grain surface area.